A typical prior art sensing system uses single-frequency (narrowband) transducers and time delay estimation to determine distances to locations in a scene. Frequently, the narrowband pulses have a center frequency around 40 kHz and bandwidth of 1-2 kHz, i.e., e.g., the pulses operate in the range of 40 kHz±1 kHz.
Specifically, the systems measure a time delay between transmitted and received pulses. The time delay is multiplied by the speed of the pulses to estimate of the distances to the scene.
Additional information can be obtained by an array of transducers (transmitters and receivers), which transmit the same frequency pulse from each transducer with an appropriate time delay between pulses from different transducers, so that the overall transmission is essentially directed towards a particular location in the scene. This is sometimes called beam steering.
By scanning in different directions, the array can estimate the distances to different locations in the scene. That approach is similar to methods used in medical ultrasound. That approach requires a large number of transducers, or different transducers locations to make an effective array. Furthermore, that scanning approach requires multiple pulse transmissions, one for each direction of the beam, which increases the time before the scene can be sufficiently reconstructed. Also, it is not straightforward to form a virtual, array by moving the array elements because the array moves.